Fertilization of mammalian ovum by sperm is a complicated multistep process involving binding of sperm to the egg, induction of the acrosome reaction (an exocytic activation of the sperm) and penetration of the sperm through the zona pellucida. Our laboratory has made the new observation that bombesin-like peptides appear to be endogenous regulators of the primate acrosome reaction. The bombesin-like peptides are a unique, wide-ranging family of peptides originally found in frog skin and later characterized in mammals. The mammalian bombesin-like peptides, of which gastrin-releasing peptide (GRP) is the best characterized member, are important neurotransmitters, growth factors, and paracrine hormones. The role of GRP as a potential regulator of the growth of small cell lung carcinoma has been widely studied. Previously our laboratory has characterized the genes and cDNAs encoding GRP and the GRP receptor. We have made the new observation that a splice variant of the GRP mRNA is expressed in primate testes and encodes a new bombesin-like peptide that is capable of inducing the acrosome reaction. Preliminary studies in vitro have shown that 1) bombesin-like peptides stimulate the acrosome reaction in both rhesus monkey and human sperm; 2) that specific GRP receptor antagonists block this stimulation and also block the progesterone-induced acrosome reaction in monkey and human sperm, and 3) that GRP antagonists inhibit the fertilization of monkey oocytes by sperm in in vitro fertilization (IVF) assays. The purpose of this grant is to characterize the role of bombesin-like peptides in the acrosome reaction and fertilization of primate ova by sperm. Specifically, we propose: 1) to characterize the endogenous bombesin-like peptide(s) which induce the acrosome reaction; 2) to characterize the bombesin-like peptide receptor expressed in sperm; 3) to characterize in vitro the conditions, time course and mechanisms by which bombesin agonists stimulate and bombesin antagonists inhibit the acrosome reaction in sperm; and 4) to investigate the potential role of bombesin- like peptides in fertilization using in vitro fertilization of monkey oocytes by monkey sperm. The bombesin-like peptides and receptors will be characterized by molecular and conventional techniques. Studies on the role of bombesin-like peptides on fertilization will take advantage of the ongoing rhesus monkey IVF program at the Oregon Regional Primate Research Center. Thus, the aim of this research is to characterize a new intermediate step in the fertilization of ova by sperm and to generate potential new approaches to problems of human fertility and contraception.